I was a Member of special interest house at RIT's school of photography a couple decades ago.

Between Canon and Nikon, Canon was preferred by students 9 to 10, because it was thought to have higher durability. Most new cameras had gaffer's tape applied to logos and any shiny parts right out of the box, so it wasn't like people we touting brand - they just went with what they thought would last a trip to initial dessert storm, caving trip to WA, etc...

the 70-200 f/2.8 without IS cost, $1300, the same lens with IS cost $2000. So all the tech can certainly be accommodated at a 'pro IS level' with a $700 up-charge, maybe a touch more if they want to add special coatings of what not to the is lens element.

As always, everything is a package deal....lets not discount the added reach the 24-105L offers with IS and decent IQ and contrast.

24-105 has added reach, but also added distortion and a 70-200/300 lens delivers much better 70-105mm quality plus a LOT more reach.

Thing is, 24-105 covers a lot of range as a quality walk around lens. No doubt a pair of lens (like a 24-70 & 70-200) give you more in multiple metrics, namely quality & reach, but one len / one body has it's benefits for casual trips where you don't even take a bag... That's why I like my 24-105.

When I was in photo school in late 80's, early 90's, the general thought was that the third party lenses were almost canon quality, the main reason you'd pay canon money was to retain strong re-sale value.

Although I have yet to buy a non canon lense in all these years - it seems like one has to strongly consider tamron / sigma options after looking at these canon prices.

I've owned the non-L version of the lens many, many years... wonder lens. I've never thought of upgrading to L because I couldn't imagine a sharper lens, and to me, the IS hold little value as nearly all macro must really be done on a tripod...

I'm curious about the difference the rounded aperture blades of the L makes - I can't say I've ever been bothered with the non-L's effect, but it would be interested to see an A - B comparison between the lenses that highlights this difference.